Concentrated sulfuric acid (0.5 mL) was slowly added dropwise to a solution of 3-hydroxy-4-nitrobenzoic acid (1.88 g, 10.3 mmol) dissolved in undried HPLC-grade methanol (60 mL), and the reaction mixture was subsequently heated to reflux for 18 hours. Upon completion of the reaction, sodium bicarbonate was added to the reaction solution to neutralize the acidity, followed by evaporation of the solvent under reduced pressure. To the residue, water and ethyl acetate were added for extraction and the aqueous layer was separated. The aqueous layer was further extracted five times with ethyl acetate. All organic layers were combined, washed twice with saturated brine, dried over anhydrous magnesium sulfate, and finally concentrated under reduced pressure to remove the solvent to give methyl 3-hydroxy-4-nitrobenzoate as yellow crystals with a yield of 2.00 g (99% yield) and a melting point of 89.5-90.5°C (literature values: 86-88°C, 91-92°C). UV spectrum (methanol): λmax = 238, 270, 351 nm. infrared spectrum (ATR): ν = 3310, 3124, 3050, 2962, 2842, 1720, 1622, 1587, 1521, 1476, 1434, 1323, 1283, 1222, 1147, 1098, 1067, 967, 891, 843, 798, 780, 743, 666 cm-1.1H NMR (500 MHz, CDCl3): δ=3.96 (s, 3H), 7.61 (dd, J=8.8, 1.7 Hz, 1H), 7.83 (d, J=1.7 Hz, 1H), 8.17 (d, J=8.8 Hz, 1H), 10.50 (s , 1H).13C NMR and DEPT (125 MHz, CDCl3): δ = 53.08 (CH3), 120.73 (CH), 121.80 (CH), 125.41 (CH), 135.90 (C), 138.10 (C), 154.79 (C), 164.97 (C=O). Mass spectrum (ESI, -10V): m/z=196 ([M-H]-). Calculated elemental analysis (C8H7NO5): C 48.74%, H 3.58%, N 7.10%; measured values: C 48.58%, H 3.44%, N 7.25%.
